Libertarians believe that strict determinism and freedom are incompatible. Freedom seems to require some form of indeterminism.

"Radical" libertarians believe that one's actions are not determined by anything prior to a decision, including one's character and values, and one's feelings and desires. This extreme view, held by leading libertarians such as Robert Kane, Peter van Inwagen and their followers, denies that the will has control over actions.

Critics of libertarianism properly attack this view. If an agent's decisions are not connected in any way with character and other personal properties, they rightly claim that the agent can hardly be held responsible for them.

Most libertarians have been mind/bodydualists who, following René Descartes, explained human freedom by a separate mind substance that somehow manages to act in the physical world. Some, especially Immanuel Kant, believed that our freedom only existed in a transcendental or noumenal world, leaving the physical world to be completely deterministic.

Religious libertarians say that God has given man a gift of freedom, but at the same time that God's foreknowledge knows everything that man will do.

In recent free will debates, these dualist explanations are called "agent-causal libertarianism." The idea is that humans have a kind of agency (an ability to act) that cannot be explained in terms of physical events.

One alternative to dualism is called "event-causal libertarianism," in which some events are uncaused or indeterministically caused. Note that eliminating strict determinism does not eliminate causality.

We can still have events that are caused by indeterministic prior events. And these indeterministic events have prior causes, but the prior causes are not sufficient to determine the events precisely. In modern physics, for example, events are only statistical or probabilistic. We can call this soft causality, meaning not pre-determined but still having a causal explanation.

Still another position is to say that human freedom is uncaused or simply non-causal. This would eliminate causality. Some philosophers think "reasons" or "intentions" are not causes and describe their explanations of libertarian freedom as "non-causal."

We can thus present a taxonomy of indeterminist positions.

It is claimed by some philosophers that libertarian accounts of free will are unintelligible. No coherent idea can be provided for the role of indeterminism and chance, they say. They include the current chief spokesman for libertarianism, Robert Kane. 1

The first libertarian, Epicurus, argued that as atoms moved through the void, there were occasions when they would "swerve" from their otherwise determined paths, thus initiating new causal chains.

The modern equivalent of the Epicurean swerve is quantum mechanical indeterminacy, again a property of atoms. We now know that atoms do not just occasionally swerve, they move unpredictably whenever they are in close contact with other atoms.

Everything in the material universe is made of atoms in unstoppable perpetual motion. Deterministic paths are only the case for very large objects, where the statistical laws of atomic physics average to become nearly certain dynamical laws for billiard balls and planets.

Many determinists are now willing to admit that there is real indeterminism in the universe. 2,3 Libertarians should agree with them that if indeterministic chance was the direct direct cause of our actions, that would not be freedom with responsibility.

Determinists might also agree that if chance is not a direct cause of our actions, it would do no harm. In which case, libertarians should be able to convince determinists that if chance provides real alternatives to be considered by the adequately determined will, it provides real alternative possibilities for thought and action. It provides freedom and creativity.

Libertarians should give the determinists, at least the compatibilists, the kind of freedom they say they want, one that provides an adequately determined will and actions for which we can take responsibility.

Accounts of free will purport to tell us what is required if we are to be free agents, individuals who, at least sometimes when we act, act freely. Libertarian accounts, of course, include a requirement of indeterminism of one sort or another somewhere in the processes leading to free actions. But while proponents of such views take determinism to preclude free will, indeterminism is widely held to be no more hospitable. An undetermined action, it is said would be random or arbitrary. It could not be rational or rationally explicable. The agent would lack control over her behavior. At best, indeterminism in the processes leading to our actions would be superfluous, adding nothing of value even if it did not detract from what we want.

2. Honderich, Ted (2002), How Free Are You?, p.5.

"Maybe it should have been called determinism-where-it-matters. It allows that there is or may be some indeterminism but only at what is called the micro-level of our existence, the level of the small particles of our bodies."

3. Searle, John (2004), Freedom and Neurobiology, p.74-75.

"First we know that our experiences of free action contain both indeterminism and rationality...Second we know that quantum indeterminacy is the only form of indeterminism that is indisputably established as a fact of nature...it follows that quantum mechanics must enter into the explanation of consciousness."